Mad Cow Tomach Build

[Issus]

I'm starting to build my Tomach, 54mm minimum diameter fibreglass rocket.

I'm going to build this as the manufacturer recommends for once, except using Techniglue R5 as I can't source Cotronics or Aeropoxy - and i'll be doing tip to tip carbon with 94gsm carbon cloth on the fins.

So far, I've encountered a few issues:
* The milling on the fins and CR's was pretty terrible. There are 0.2+mm sections of glass which has not been milled at the bottom so I've had to file that off as it was too thick to sand.
* Was missing the airframe ring for the AV bay in the kit. I put the forward airframe section in the lathe cut it down. When it was down to 0.05mm of glass left i finished it off with the dremel.

I have the AV bay bulkplates drilled and the double one epoxied together:

The nosecone coupler and AVBay coupler are now bonded. I've wrapped tape (normally i'd use fibreglass tape but i couldnt find) around where they stop to keep epoxy off, and also to allow it to be cured vertically without the epoxy leaking out.

 

[chuck5395]

Subscribed. I'll be watching your build with great interest.
I'll be starting my own here shortly.

 

[mrhp]

subscribed

 

[Issus]

When cleaning up the epoxy on the nosecone, I found it isnt quite round. With the base revolving on the lathe (base of the nosecone, not the coupler that is) perfectly, and the tip revolving perfectly centred the nosecone has a definite off axis section towards the front. Slightly disconcerting but hey, it's on my meant to go mach 2, so what does it matter.

I need to build a fin bevelling jig - normally I do this when cutting the fin out on the CNC router so i'll have to make one to do it manually as I don't have a belt sander. I've seen some nice designs around which i'll probably replicate.

This seems like it's going to be a ridiculously quick and easy build though



Any thoughts on motor retention? I don't really want to use a MD motor retainer as those limit you to one case size (unless you get heavy spacers). I'm thinking of just friction fitting it?

 

[awseiger]

A method I've been thinking about is mounting some pem nuts in the body tube and then retaining the motor with 3 set screws in the body tube. Not so nice on the motor, but it's an alternative. It's like a super friction fit.

Could also use set screws to hold the MD retainer at different spots in the body tube. This leaves holes, though.

 

[Issus]

Also, as a note, the instructions dont say how far apart to drill the holes in the bulkheads on the AV bay, I've drilled them 32mm from the centre of the plate - ie: 64mm between centres.

 

[webtech]

subscribed

 

[Issus]

The AV bay goes together nicely, I still need to file the bulkheads down a little more. I wont be securing any nuts with glue until i've post cured the epoxies in this.

I'm starting to regret building this as the manufacturer specifies. Doing away with the bolt in the nose cone and having a threaded rod would have been very nice for allowing a tracker to be put in the nosecone (using a threaded rod to the nose, with an eyebolt on the base). Alas I wanted to do things the way the manufacturer specifies so now I'll have to get the tracker in the AV bay - no big deal at all.

I need to get this put into Rocksim, openrocket or rasaero because I think the default fin position is going to be wildly unstable and require a ton of nose weight (I have the 30" version btw). I think this is going to need a static stability margin of 2.5-3 to still have any stability left at Mach 2 (which I dont think i can build light enough to reach.)

 

[Issus]

My tower launcher has been modified for handling this rocket without ripping it's fins off: https://www.rocketryforum.com/showt...power-launch-tower-design-review&goto=newpost



Rocket in the tower is obviously not the tomach

 

[Issus]

Still trying to think of ideas for avoiding a Aeropac retainer.

Firstly, my issues with the aeropac:
* With a CTI motor case (what I have) - It must be installed with a reload in the motor. I don't have a dangerous goods license so I can only obtain motors at a launch and use them. Ideas to overcome this so far are to take a forward closure from a spent motor, or a new reload home to do it, or to do final rocket assembly at a launch (not really ideal). I would have to make spacers the same size as a the grains and nozzle for this however.
* Must mount it for the maximum size case you want to use, and use an adapter to use any smaller cases (more money...) - If i want to be able to fly 6GXL loads but mostly run on 5 or 6 grain this is less than ideal.

On the plus side, they are really very nicely made and convenient.

We've mentioned holding the case in with screws which is a great idea but I do wonder about drilling holes for this, and making short enough screws - plus how well the glass will hold up to making the screws tight without stripping/grinding away the thread.

My biggest worry with friction fitting it is that this rocket will need shear pins to hold the AV bay to motor section, otherwise it could go its on way on burnout which is obviously very bad. With shear pins, I'm worried the ejection charge to shear them will instead push the case out, and I still dont have a way to attach the recovery harness.

What does everyone think of a solid bulkplate with an eyebolt or U bolt on it, perhaps with a small vent hole as well installed forwards of where the 6GXL case would hend? This would allow the recovery harness to be attached to it, and friction fit the motor case. The motor case shouldn't see much trying to pull it out unless it gets swung hard on recovery (ie: main coming out) A single screw through the airframe onto the case could make doubly sure it doesn't decide to go it's own way. I'd inclined to mill one out of aluminium plate, or 6mm plywood with several layers of carbon kevlar laminate (lighter and stronger, easier to bond).

 

[awseiger]

You could always roll your own minimum diameter retainer. I know the thread size for the CTI threaded closure is published, and I'm sure you can make spacers from coupler nuts.

I know my club does not allow friction fitting in anything but the smallest Estes motors. There's a good reason for it too... It doesn't work.

What about a small bit of all thread along each fin. Just tighten down the nut. It's not pretty, and a little bit draggy, but it's an option as well. I think I saw someone doing this somewhere.

There's also the slimline retainers, which won't look awful if you glue it externally. Better than the aeropack, at least.

 

[Issus]

Thanks for your thoughts awseiger. The thread size is 5/16-18 (https://www.aeropack.net/min_dia_retainers.asp).

It's only a 3" length to adapt from 6G to 6GXL, and i feel this could be done lighter with a little bit if aluminium done on the lathe and some composites.

Your allthread idea is very interesting. Does this go in the fillet? If it's done right with a low profile nut i bet this could be done without any drag penalty. It would however preclude the use of a tailcone aft closure though, which i'm quite interested in trying. It wouldn't work on this rocket because of the tailcone but it's a really interesting idea to keep in mind for the future!

I don't like the idea of an external retainer, the drag penalty and inability (as far as i'm aware) to use a tailcone closure is too much.

How about motor ejection? Solves a bunch of issues if the motor is meant to come out!

 

[DRAGON64]

This is an awesome performance based design, I can't wait to see what your final look is going to be.

 

[chuck5395]

I'm on the verge of ordering the Slimline for my Tomach.
I hesitate on the Aeropack Bulkhead retainer because I loose flexibility. Looking at this rocket in OpenRocket, there are a number of 38mm motors that would perform well with this rocket. Can't do that if I go with the bulkhead retainer. The Slimline does attach to the outside of the body tube, but does offer some other benefits.

 

[Issus]

Few updates.. nothing more built though (working 19hr days at the moment.. sigh)

I ordered an AeroPack retainer from MadCow with my Frenzy XL, hopefully it will get in in 1.5 weeks or so.

I'm thinking i'll do the nosecone something like a PML Intellicone. This will let me still put electronics in if I want, and if not - will add more weight up front at least. I'm thinking a 38mm tube (I'm sure I have some 38mm bluetube around?) with carbonkevlar laminated plywood centring rings. Failing that I might just use some 2mm Carbon but it seems like a waste of material. I'll run a kevlar U through the CR's for shock cord and chute attachment.

 

[Issus]

Some progress... more in need of advice though

Seeing as my large CNC mill is getting upgraded right now (redoing the electronics system and bed)... I can't do fin bevels the usual way as i stated before. To that end, I bought a 230mm disc/150mm belt dust generator.. err linishing machine.


I came up with what I thought at the time was a rather ingenious idea. Obviously the work support of the machine doesn't go to 80 degrees (required for a 10 degree bevel on the fins). Therefore, I sanded a block of scrap down to 10 degrees and will then hold the fin in that to push up against the disc or belt.

First problem: how do I secure it.
First solution! Put a bit of MDF scrap on top, use a cross dowel and a 6mm bolt, then put a washer on it which will sit over the fin and pull down on it. Perfect right?

Second problem: All the force is in the one point on the fin, and with nothing on the other side of the washer it sticks the fin out an extra few degrees. As the fin is not a straight piece it also sticks one end out further than the other.
Second solution! I need a spacer on the other side of the washer. After looking around a bit i spotted a likely piece of scrap acrylic. Acrylic is too fat. So i put it on a fast diet with the disc (turns out that Acrylic makes awesome disc cleaner btw).



Third problem: Washer still put too much force in the middle giving it a slight bow (must be compressing the wood or something).
Third solution! Make a big tongue of that scrap aluminium plate sitting next to the drill press! Perfect, the fin edge is all flat and looks great. It's like a giant hand plane.. that goes into a sander.. so isnt really much of a handplane at all really.

So, now to mark the area to remove material from. Black marker half way down the fin works perfectly.


Ready to go. Right?


Forth problem: Bolt head really isnt high enough, so it's sticking out too far which makes it so the head sticks into the way of the belt/disc.
Forth solution: File it down a bit, then just sand it anyway.



End result: One very hot, very thin bolt head, fin that has not been sanded at all.

Conclusion: I rely on Solidworks, CAM and CNC tools far too much!


So, how does one put a 10 degree bevel on a fin when you don't have a robot to do your bidding?

 

[Issus]

Will try this: https://www.jcrocket.com/finbevels.shtml tomorrow. Seems simple enough

Dad has stolen my router table, so it's at his house - just as well as that was going to be my way of bevelling the fins before I used this as an excuse to go buy the sander (tabbed parts from the mill will no longer be annoying!)

 

[Issus]

So, work got in the way during the week, however yesterday I was able to spend most of the day playin... err working.. out in the workshop.

I built the fin bevelling jig, works very nicely. My support table is not as solid as i'd like and so it jiggles around a little bit when the sander is going so I needed to set the bevel back a little and finalise it with the belt manually. It made life a lot easier though.

Then, I marked out the area where the fins will attach (60mm from bottom of the tube for me) and 60 grit sandpaper was liberally applied to rough up the surface. I also roughed up the fin surfaces.

I used the belt (not running) to completely flatten off the edge of the fin which attaches to the body tube. My previous work filing still had them not quite perfect. Techniglue R5 will only create a structure bond between surfaces 0.5mm or closer so this is important.

Once everything was washed down with first Methylated Spirits (denatured alcohol for you North Americans), and then with acetone to ensure it was dust free and skin oil free, I mixed up some Techniglue and applied it to the root edges of the fins. Using the included laser-cut cardboard (couldn't supply plywood??) alignment jig and some elastic bands the fins were fitted. As the slots in the card are a little bit large I spent quite a bit of time ensuring the fins were both vertical and aligned down the tube.

After the epoxy gelled, I set to work curing it a bit faster. I couldn't be bothered pull the oven out from where it resides so I simply put the end of a hair dryer against the end of the tube (the hair dryer exhaust is pretty much exactly the same size) and ran it on high temp, slow fan. This got the tube to about 62C, but i needed it hotter. I wrapped a couple of layers of glass cloth around the tube and fins which raised the temperature to 75c on the outside of the airframe. I left this for 4hrs and came back to a nicely cured (still needs to go in the oven later) set of fins.

 

[patelldp]

Looks great! I think that this kit is the new Three Dogs Kestrel.

Go to www.3dogsrocketry.com and buy their 8/32 anchors for the altimeter bay. Save some weight and it will be more than adequate strength wise. I just utilized these for my LOC Lil Nuke Pro Maxx, pics attached.

 

[majordude]

Dad has stolen my router table, so it's at his house - just as well as that was going to be my way of bevelling the fins before I used this as an excuse to go buy the sander (tabbed parts from the mill will no longer be annoying!)

This is one of the prettier rocket designs I have seen and your craftsmanship is off the charts.

You sanded those fins by hand? WOW. They look great!

I am wondering... you have a CNC machine? You usually use that to bevel fins or am I missing something?

I want to outsource my work. Are bevels CNC-able?

When will this fly?

 

[CCotner]

Looks great! I think that this kit is the new Three Dogs Kestrel.

Go to www.3dogsrocketry.com and buy their 8/32 anchors for the altimeter bay. Save some weight and it will be more than adequate strength wise. I just utilized these for my LOC Lil Nuke Pro Maxx, pics attached.

I wish they offered it with a long enough tube for the 6GXL case... if they did it truly would approach/best the quality and performance of the KestraL, given its thinner/lighter fiberglass airframe (like the KestraL) compared to normal 54mm fiberglass (like the Space Cowboy).

 

[Issus]

I am wondering... you have a CNC machine? You usually use that to bevel fins or am I missing something?

I want to outsource my work. Are bevels CNC-able?

When will this fly?

I normally scratchbuild everything, so i can put in a plate of glass/carbon/plywood and 3d mill in airfoils or bevels without any difficulty. I just design the airfoil in solidworks (Von Karman, NACA symetrical, "that looks good enough", or any other profile) then just output it in CAM. The machine does its job and i get nice polished airfoils The difficulty arises when buying kits. Holding down a workpiece with no extra area around it can be difficult, but not impossible - however I would have to scan or very accurately measure the fin, cut out a pocket on some scrap for it to sit in for positioning, and then model the fin in solidworks and machine it. Its an awful lot of work - far more than just making them from scratch!

What would be easier is to just build a jig for a disc sander or router table.

I got heavily distracted by another rocket (designed, built and flown in the past two weeks )

I don't know when this will fly - i'm hoping to fly it over june 1st/2nd long weekend campout launch however my Frenzy XL is my priority as it was purchased for me, along with the motor (M2250) and this is one of two launches of the year I could fly it at. I really just need to do the T-T glass + av bay on this and it should be good to go.

My 54mm MD retainer arrived, and I now have a spent 54mm forward CTI closure to make the adapter from for gluing it in place. I need to get to that at some point

I have the fillets done on the tomach now.

First step, mark out the fillets then mask the "overflow" area.

Techniglue R5, West colloidal silica and carbon fibre tailings from the lathe make the paste for my fillets. There are some little slivers of aluminium in there which got mixed with the CF haha - oh well.

Baking paper and dowels squish the excess epoxy mix out and give a perfect radius with a smooth surface.

One with tape removed, one without - the black line on the edge of the tape on the right hand one is CF stands on the surface

Before the epoxy is completely cured, the tip and tail of the fillet is shaped with a file. Takes about 30 seconds per fillet.

 

[Issus]

Is the rocket i was distracted by, ~4800ft on a CTI K360 6G 54mm.

 

[chuck5395]

Looking good. I gotta get mine started soon.

 

[Issus]

So, Once again I've been distracted by another rocket build (I had a Frenzy XL and M2250 donated to me.)

Anyway, I have made a bit more progress, and will be making more each night this week with just the 2nd colour of paint left on the frenzy. I'm hoping to launch the Tomach this weekend, Sunday morning I have a 2hr window to 23500ft which will let me put a K1440 which I've ordered in this. I wanted to fly this on a L, but I was silly and didn't buy the longer airframe version! It's still expected to see about mach 2.3, but I'll be happy with Mach 2.

So, Fin templates for glass and carbon kevlar are made by sticking paper from the back side of the fin, as tight as possible against the curve of the fin/airframe.

Then transferred to something a bit more rigid for drawing around on cloth. An old box works perfect.

Using a jig I made for this rocket

I can pull a vacuum on the whole assembly (only -15hg.. approx 7psi? due to leaks)
[/img]https://www.markhphoto.com.au/Rocketry/Tomach-Build/i-PP5g47b/0/L/IMG_1421-L.jpg

And with my $10 heater, get the resin flowing out nicely. The jig, obviously, does not fit in an oven.
[img]https://www.markhphoto.com.au/Rocketry/Tomach-Build/i-kkRxMDJ/0/L/IMG_1420-L.jpg

The layup is one 45 degree layer of 180gsm glass, one layer of 0 degree 180gsm glass, and a layer of 0 degree unknown weight carbon kevlar.. all plain weave. Perforated film and breather on top. This jig is a *huge* pain in the proverbial to seal up against a vacuum. I ended up using mastic all around then then pulling a vacuum on it with a shop vac - then adding hot glue around the mastic. The shop vac doesnt pull a very good vaccum but it does have a HUGE flow rate, so it pulls the hot glue through any gaps and seals everything up nicely. Then I switch over to the vacuum pump assembly (auto cycling, a few dozen litres of vacuum reservoir) which is only about 5.5L/min vs the shop vac's 200+L/min.

Due to the vast amount of setup time this took, almost all of which was sealing it up.. and the amount of other work and building I need to do before the weekend I have a feeling that the other two fins are going to get a 25kg sack of KNO3 dumped on them for weight rather than vacuum. Better than nothing, faster than a vacuum.

 

[DRAGON64]

That bird is coming along nicely... you layup jig looks sweet. can it be made adjustable for other airframes?

 

[Issus]

Thanks - and of course it is adjustable It's based on John C's jig https://www.jcrocket.com/tttjig.shtml
Mine has no blind nuts, and uses knock down nuts for assembly/disassembly and was designed for cutting with a CNC mill. My top is also varnished and waxed MDF (also part of my seal issue.. nothing sticks!). The MDF i have was milling so horribly - it was a pallet coversheet, not a quality piece of MDF, that I had to switch to plywood for the frame. PM me if you want the solidworks files or PDF's of the parts layed out for cutting.

Waiting for some paint to get touch dry out in the workshop before i go do the next set of fin fillets. Need to find a nice pliable bag to pour the 25kg of weights into, the sack it comes in is not going to mould to the fins very well.

 

[Issus]

I present the "i cant be bothered pulling a vacuum on this" approach.

Also started making a CTI-> Aeropack MD retainer. I can't get the proper ones here, and shipping costs more than the adapter to get it from the USA.. soo I'm doing my own. Our Prefect and RSO dont really like the idea of the ones that screw into the ejection well, So I'm going to make one that goes around the outside and has 2-3 grub screws to secure it. CTI were nice enough to mould in a ridge which is perfect for this.

This is my prototype, it bored it too deep and tapped the thread on an angle (i'm really terrible with taps!) I've since tapped a new one nice and straight, but still need to bore it out.

 

[rocketgeek101]

Very very nice build. Your work is truly fantastic. Have you got a paint scheme in mind?

 

[Issus]

Thanks! This rocket has been a bit of a halfass effort to be honest.

I have to putty and prime it tonight, painting tomorrow.. so it's amazing paint scheme is going to be "left over red acrylic paint" Hopefully there is enough left in the can to get full coverage. Hopefully there is enough primer left to get full coverage too haha. I've gone through 8? cans of paint/primer in the past week - can't use the aircompressor at night but i can use spray cans! I'm not going to bother buying new paint for it - if it does go M2+, it will need to be stripped and repainted before it's next flight, so there isn't any point.

Last night I sanded back the fins just to the point of hitting the cloth then put a coat of epoxy over it to give me something to sand off - I just love sanding so very much - to try and fill the weave of the cloth, mostly on the fin I vac bagged. The fins that were weighed down came out fairly flat without a weave in them - not enough pressure on them to get the cloth pattern to show when using perf-film. I'm almost out of sand paper too, I've gone through about 5 metres of that this past week too.

The CTI retainer adapter is also complete, I just need to get some M4 grub screws for it. My M4 tap is my nicest one, costing almost as much as my whole UNC set, and screwed in beautifully, easier than putting in the grub screw will be. Therefore I only went with 2 holes, because I didn't bugger one up I'll post pics and a proper write up tonight on that. I'm very happy with how it turned out, other than the big gouge in it where I didn't do the chuck up tight enough

AV bay is also built, but needs wiring, hoping to do that tonight since my other plans (building a CTI M2250) got postponed until tomorrow.